Devices for robotically dispensing sealants and adhesives on to parts have become increasingly popular in recent years.
Products such as Graco""s PRECISIONFLO unit using technology such as shown in U.S. Pat. No. 5,847,285, the contents of which are incorporated by reference, have become increasingly popular with automotive manufacturers in order to provide precision application of a bead of (single component) adhesive for various applications. Such units typically dispense at pressures ranging from around 600 PSI to 3000 PSI. Recently, the material manufacturers of such sealants and adhesives have been producing plural component materials which provide increased performance for the manufacturer.
It is therefore an object of this invention to provide a dispensing apparatus which is capable of dispensing such plural component materials with the same precision as the single component products and yet will maintain ratio assurance and integrity for mixing the two materials.
Various parties involved in such manufacture use different terms for the materials involved. The major component of the plural material is also commonly referred to in the industry as the B component or the resin component. Similarly, the minor component is also often referred to as the A component, or activator, or catalyst.
Overall, the scheme can be characterized by saying first look at the flow rate. If the flow rate is too high, decrease is needed on one of the components so the ratio error is then looked at and the flow rate/pressure differential for the material which is there in excess is decremented. Another level of control is provided in that the ratio error is continually examined and the direction of the ratio error is used for additional control. This provides very precise control of ratio and flow and helps prevent oscillation, hunting and other undesirable characteristics in such a system.
These and other objects and advantages of the invention will appear more fully from the following description made in conjunction with the accompanying drawings wherein like reference characters refer to the same or similar parts throughout the several views.